Automatic Dishwashing is a demanding field in which specialized detergent formulations are required to deliver efficient and effective sanitization and cleansing of dishware, including stain removal and tough food cleaning. Automatic dishwashing has some unique constraints as compared to fabric laundering; for example, spotlessness and lack of film on glasses and silverware is particularly important. In many laundering operations, in contrast, there is a tolerance for substances which may be greasy, oily, soapy or lubricious, often fabric softeners or fatty acid salts, being deposited on the substrate being cleaned.
In modem automatic dishwashing formulations, tough food cleaning performance is essential, and this is commonly accomplished by detersive enzymes. Alkalis are also used, but may be highly corrosive, especially at high levels. Stain removal, for example of stains deposited by hot beverages such as tea, coffee or the like is especially sought after by the consumer. This is commonly accomplished by a variety of bleaches.
Several aspects of automatic dishwashing detergent compositions are markedly different from laundry compositions. For example, special nonionic surfactant types are used owing to the very low tolerance for foam production in domestic spray-arm dishwashers; and builder systems tend to include significantly different silicates from those commonly used in laundry compositions.
Owing to the enzyme-deactivating nature of some of the most effective bleaches, especially hypochlorite bleaches, compromise detergent formulations have often been provided. This includes formulations in which a relatively mild and enzyme-compatible hydrogen peroxide source, such as sodium perborate, is combined with the enzymes; optionally with tetraacetylethylenediamine as a bleach activator.
Various efforts have been made to improve the efficacy of bleach activators and hundreds of such activators have been described in the literature; however, at present, only tetraacetylethylenediamine (TAED) appears to be commercially available in an automatic dishwashing composition. Reasons for the lack of commercially successful improvements may include that the thrust of bleach activator development efforts has been directed to improvements for laundry compositions which are not easily adaptable for automatic dishwashing. Bleach activators may, for example, yield foam-forming or malodorous peracids, neither of which are acceptable for automatic dishwashing in a spray-action domestic dishwasher. Unfortunately, there has been little teaching in the art as to which of the now so numerous bleach activators would be problem-free in the unique automatic dishwashing context. Other possible explanations for the lack of success of new bleach activators in automatic dishwashing is that certain improved bleach activators may, though they effectively improve bleaching and stain removal, have undesirable tendencies to deposit on the dishware; or they may simply be too costly or mass-inefficient.
The disclosure of many bleach activators in the context of laundry formulations includes the suggestion that quaternary substituted versions of such activators may indeed be of a depositing nature and have desirable fabric conditioning properties. See, for example, U.S. Pat. No. 4,751,015 at col. 3, lines 22-27. In light of this teaching and in view of the recognized need to minimize deposition tendencies of ingredients in automatic dishwashing, the automatic dishwashing detergent formulator would be inclined to avoid such bleach activators. This patent as well as EP 427,224 and EP 408,131 are also illustrative of disclosures of bleach activators which may include chemical groups which may be cationic and/or which may form peroxycarbonic acids when perhydrolyzed.
Among the many efforts which have been made to improve bleach activators for laundry purposes, it has been disclosed that diperacids can have beneficial effects, though there is not apparently any particular direction to the effect that di- or multiperacids, let alone cationic or anionic versions thereof, would be particularly useful in automatic dishwashing. See, for example, Kirk Othmer's Encyclopedia of Chemical Technology, 4th. Ed., 1992, John Wiley & Sons, Vol. 4, ppg. 271-300, "Bleaching Agents (Survey)" which includes reference to diperoxydodecanedioic acid (DPDA) and its homologs. Such compounds have the formula HOOC(O)(CH.sub.2).sub.n C(O)OOH wherein n is typically 10 but can in general range more widely. Although the peroxy moieties of the diperacid are ionizable and hydrophilic, such diperacids contain in addition only a non-hydrophilic aliphatic "spacer", --(CH.sub.2).sub.n --, separating the two peracid moieties. In short, they do not contain peroxide-free hydrophiles of the types and substitution patterns described hereinafter. By way of additional diperacid disclosures, EP 68,547 describes aromatic diperoxyacids. U.S. Pat. Nos. 5,071,584, 5,041,546 and EP 316,809 describe heterocyclic polypercarboxylic acids and/or salts of amino-polypercarboxylic acids. As in the case of DPDA, such compounds lack a strongly hydrophilic moiety situated in-between the peracid moieties.
Another ongoing need in the art of automatic dishwashing is the provision of more effective formulations of the so-called "compact" type: such compositions should preferably deliver uncompromised levels of performance while using lower levels of detersive ingredients. Desirably in view of legislation in certain geographies, such compact formulations should be free from phosphate builder.
It is accordingly an object herein to provide an improved automatic dishwashing detergent comprising particularly selected bleach activators, preferably in compact nonphosphate granular form accompanied by certain water-soluble silicates, low-foaming nonionic detersive surfactants particularly adapted for automatic dishwashing use, particular detersive enzymes, and other automatic dishwashing compatible ingredients, all formulated to deliver uncompromised levels of cleaning and stain removal without undesirable spotting/filming, odor or foaming deficiencies. Other objects include the provision of improved bleach activators for automatic dishwashing.